Processing method for recovering iron oxide and hydrochloric acid

Abstract

A method of processing waste iron chloride solution including ferrous chloride, ferric chloride or mixtures thereof and optionally free hydrochloric acid, includes concentrating waste iron chloride solution into concentrated liquid having iron chloride concentration of at least 30%-40% by weight; optionally oxidizing ferrous chloride in the concentrated liquid from the concentration step to ferric chloride providing liquid containing ferric chloride; hydrolyzing the liquid containing ferric chloride from the oxidation step at 155-350° C., maintaining the ferric chloride concentration at least at 65% by weight, generating steam containing hydrogen chloride and liquid containing ferric oxide; separating ferric oxide from the liquid containing ferric oxide in the hydrolysis step; condensing steam containing hydrogen chloride in the hydrolysis step, recovering hydrochloric acid at a concentration of at least 10%-15% by weight; and using condensation energy of the hydrogen chloride containing steam in the recovery step to heat the concentration step performed under reduced pressure.

The invention claimed is: 
     
       1. A method of processing a waste iron chloride solution including ferrous chloride, ferric chloride or possible mixtures thereof and optionally free hydrochloric acid, the method comprising the following steps:
 in a concentration step, concentrating the waste iron chloride solution into a concentrated liquid having a total iron chloride concentration of at least 30% by weight; 
 in an optional oxidation step, oxidizing ferrous chloride contained in the concentrated liquid obtained from the concentration step into ferric chloride to obtain a liquid containing ferric chloride; 
 in a hydrolysis step, hydrolyzing the liquid containing ferric chloride optionally obtained from the oxidation step or hydrolyzing the concentrated liquid obtained from the concentration step containing ferric chloride at a temperature of 165-175° C. while maintaining the ferric chloride concentration at a level of 70 to 80% by weight, to generate a stream containing hydrogen chloride and liquid containing ferric oxide; 
 in a separation step, separating ferric oxide from the liquid containing ferric oxide obtained in the hydrolysis step; 
 in a recovery step, condensing the stream containing hydrogen chloride obtained in the hydrolysis step to recover hydrochloric acid at a concentration of at least 10% by weight; 
 directly or indirectly using condensation energy of the hydrogen chloride containing stream obtained in the recovery step as a heating source for the concentration step; and 
 performing the concentration step under reduced pressure. 
 
     
     
       2. The method according to  claim 1 , which further comprises concentrating the waste iron chloride solution into a concentrated liquid having a total iron chloride concentration of at least 40% by weight in the concentration step. 
     
     
       3. The method according to  claim 1 , which further comprises condensing the stream containing hydrogen chloride obtained in the hydrolysis step to recover hydrochloric acid at a concentration of at least 15% by weight in the recovery step. 
     
     
       4. The method according to  claim 1 , which further comprises adding water to the stream containing hydrogen chloride obtained in the hydrolysis step either prior to or during the recovery step and condensing, to recover hydrochloric acid from the stream at any adjustable concentration of at least 10% by weight, and using the stream containing hydrogen chloride as a heating source to provide for a temperature of at least 75° C. during the concentration step. 
     
     
       5. The method according to  claim 4 , which further comprises recovering hydrochloric acid from the stream at any adjustable concentration of at least 15% by weight. 
     
     
       6. The method according to  claim 4 , which further comprises using a condensed aqueous solution obtained from the concentration step in addition to or instead of the water added to the stream containing hydrogen chloride. 
     
     
       7. The method according to  claim 1 , which further comprises heating the concentrated liquid of the concentration step with the stream containing hydrogen chloride in an external circulation of the concentration step. 
     
     
       8. The method according to  claim 1 , which further comprises condensing the stream containing hydrogen chloride to yield a hydrochloric acid at a concentration of 20 to 35% by weight. 
     
     
       9. The method according to  claim 1 , which further comprises recirculating at least part of the liquid containing ferric oxide generated by the hydrolysis step to any previous step. 
     
     
       10. The method according to  claim 1 , which further comprises obtaining the waste iron chloride solution from pickling of steel, pre-treatment for zinc plating, leaching of iron containing ores by hydrochloric acid or etching treatment of semiconductor lead frames.